1. Field of the Invention
The present invention relates to an impurity detecting apparatus for efficiently detecting various foreign substances or impurities in a material and a detecting method therefore.
2. Description of Background Art
Tobacco leaves, a harvest, are packed in various forms as they are carried into tobacco material plants or cigarette manufacturing plants. After they are unpacked in these plants, the tobacco leaves are separated according to their varieties or mixed with other varieties. In this state, they are transported as the material for cigarettes to the next stage.
In some cases, materials in a transportation process may be mixed with some foreign substances, such as wrappers or strings used to pack tobacco leaves or some pieces of moisture-proof paper used to line packages. These foreign substances or impurities must be removed in the packages. These foreign substances or impurities must be removed in the material transportation process. To attain this, the impurities should be detected during the material transportation. If the impurities include any plastic materials that produce poisonous gases as they burn, in particular, they must be securely detected and removed.
Conventionally, a detecting apparatus with a video camera is used to detect impurities. According to this detecting apparatus, the video camera shoots the material being transported, and a decision circuit of the apparatus then detects impurities in the material according to image data obtained by the shooting. More specifically, the decision circuit detects the impurities in the materials in accordance with differences in color between tobacco leaves and the impurities.
The detecting apparatus described above can be effectively used only in the case where the colors of the impurities to be detected differ substantially from those of the tobacco leaves. If the impurities have the same or similar colors as the tobacco leaves, therefore, they cannot be detected practically.
In the tobacco leaves are of a same variety, moreover, they have their respective colors, which substantially vary depending on the quality of the leaves. In the case where the material include tobacco leaves of different varieties, in particular, therefore, it is very hard to detect impurities in them.